Implant with attached element and method of making such an implant

ABSTRACT

A tubular implant having an axial end to which is attached a ring of spoons of a material different from that of the implant. In another aspect, the invention provides a method of attaching elements to an axial end of a tubular implant comprising the steps of providing said elements on one end of a support tube having a radius substantially that of the implant in its unexpanded configuration, abutting the implant and elements end-to-end, fixing the elements to the implant; and parting the elements from the support tube. In a third aspect, the invention provides an implant carrying an element of another material, the element and implant having complementary tapered mating surfaces for achieving a taper form fit of the element onto the implant.

FIELD OF THE INVENTION

This invention relates to an implant, such as a stent formed from astent material, to which is attached at least one element, such as amarker, made from a different material, such as a material having aradiopacity greater than that of the implant material. The inventionalso relates to a method of making such an implant.

Although the present invention has particular usefulness for attachingradiopaque markers to stents, it also has application to implants(filters, for example) other than stents, and to elements other thanmarkers. Such elements could function as, for example, drug deliveryvehicles, trauma inhibitors, or connectors to link the implant toanother implant or to an implant extraction tool.

BACKGROUND ART

WO-A-95/03010 discloses a stent in the form of a metal tube having along axis, a luminal surface and an abluminal surface, and a tube wallthickness, the tube carrying within the wall thickness a radiopaquemarker made of a metal more radiopaque than the metal which forms thetube.

The stent of WO 95/03010 is created from a flat sheet of stainless steelmaterial, by photochemical etching away of selected areas of the metalsheet, to leave behind an open lattice-work pattern, which is thenrolled up into a tubular shape. A small round opening is provided ateach end of the lattice area. Into each of these openings (called“eyelets”) can be pressed a radiopaque marker of material such as gold,platinum, tungsten or iridium. The markers are positioned in the eyeletsby crimping.

EP-A-800 800 also addresses the problem of poor radiopacity of stents,but advocates a different solution. In a nickel titanium shape memoryalloy stent, it is proposed to provide, at one end at least of thecylinder which defines the stent, at least one detection element whichhas the shape of a tongue extending substantially in the longitudinaldirection of the stent, this detection element having a width, in thecircumferential direction of the stent cylinder, which is greater thanthe characteristic width, in the circumferential direction of the stent,of each of the struts which make up the lattice work pattern of thestent. It is the greater circumferential width of the tongue whichrenders it more radiopaque than the thinner struts of the lattice of thestent.

EP-A-847733 Biotronik discloses a stent which is an apertured cylinderof titanium, to each end of which is welded a meander-form ring oftantalum. The radiopacity of tantalum being much greater than that oftitanium, this construction allows the locations of the ends of thestent cylinder to be determined radioscopically.

WO-A-00/64375 ACS was published Nov. 2, 2000, that is, after the presentpriority date. It discloses a stent made from wire or tube but with endrings of a material more radiopaque that its lengthwise centre section.Materials suggested for the centre section comprise Ni—Ti shape memoryalloy (Nitinol) and stainless steel. Materials suggested for the endrings comprise tantalum, platinum, gold and platinum-iridium. To attachthe end rings to the centre section, it is suggested to use, inter alia,laser welding.

EP-A-709 068 Medinol discloses providing stent ends with “protrusionshaving enough metal therein to make them X-ray visible”. Gold andtantalum are mentioned as materials which are more visible under X-rayillumination than the stainless steel metal of the stent.

The disclosure of U.S. Pat. No. 6,022,374 is similar to that ofWO-A-95/03010 mentioned above, in that it discloses an insert ofradiopaque material within an eyelet formed in the stent. Mentioned asradiopaque materials are gold, platinum and alloys thereof.

DE-U-29904817 discloses a stent with axially extending projections atone end, at least. These projections can exhibit a thickening at theirouter cantilevered ends. This concept can be compared with thedisclosure of EP-A-800800, mentioned above.

U.S. Pat. No. 5,741,327 Frantzen discloses a stent with radiopaquemarkers attached to the ends of the body of the stent. In oneembodiment, a circumferentially continuous serpentine marker element isattached to each end of the stent. This marker element can be of gold,silver, platinum or an alloy thereof. It is disclosed that the body ofthe stent can be from a nickel-titanium alloy. The circumferentialmarker is radially expansible along with the body of the stent. Acircumferential marker is attached to an end of the stent body using oneof a number of techniques including brazing, mechanical fastening,weaving or epoxy adhesive. One specific system of attachment disclosedinvolves the use of “receivers” that extend from the ends of the stentbody. These receivers are configured to receive “tabs” provided on themarker ring. Each tab has a neck and a knob at the end of the neck andthe knob is received into a co-operating rounded space of the receiverof the stent body. A laser is used to achieve local melting so that thereceiver and tab are fused together.

The disclosures of WO 97/33534 is similar to that of WO 95/03010, inthat it includes radiopaque rivets set in a stent of less radiopaquematerial.

SUMMARY

It is one object of the present invention to provide an implant, such asa stent, with an element of different material, securely fixed to theimplant as such.

It is a more particular object of the present invention to provide anickel-titanium shape memory alloy stent with a radiopaque marker whichis compatible with the alloy of the stent; and biologically acceptable,and which is more effective and reliable than previous proposals.

According to one aspect of the present invention there is provided animplant as defined in claim 1 below. In a second aspect, there isprovided an implant as claimed in claim 17 and, in a third aspect amethod of attaching elements to an implant is provided, as claimed inclaim 16.

With a ring of elements in the form of spoons, attached at one end of atubular implant such as a stent, a more or less complete ring ofattached material is presented in the radially compact deliverydisposition of the stent, yielding potentially enhanced radiopacity.Even in the expanded disposition of the stent, a relatively small numberof wide area spoons, say four, delivers relatively good radiopacity.However, the radiopacity in the compact disposition is particularlyhigh, so that the present invention opens up the possibility toeliminate the previously indispensable radiopaque marker ring on thestent delivery system which reveals the location of an end of the stent.This in turn opens up the way to make delivery systems which are simplerin construction than the systems used up to now.

If interfitting shapes of the stent ends and attached elements are cutby a laser with its line of action always radial to the stent cylinder,then a tapered or beveled form fit between the stent and each attachedelement is achieved, enhancing the security of attachment and theprecision of placement of each element attached to the stent.

This tapered form fit is particularly helpful when it is such thatdisengagement of the form-fit occurs by a radially-outward movement ofthe element relative to the stent cylinder. This is because, when thestent expands into its installed configuration, there is radially-inwardpressure on the attached element from the surrounding bodily tissue,which resists its disengagement from the stent. This resistancecomplements and reinforces whatever other system is employed to fix theelement to the stent.

Systems to fix an element to an implant can include welding, brazing,soldering, glueing, friction welding or variations of mechanicalinterlocks and press-fit configurations.

When creating stent lattices from sheet material, tubular sheet startingmaterial is often considered advantageous. However, flat sheet materialalso is advantageous in some systems, such as those in which the stentelement is rolled up like a carpet. When laser-cutting the lattice, theabove-mentioned tapered form fit can be readily engineered when cuttingthe sheet in planar form.

In a particularly advantageous embodiment, a stent is formed from sheetmaterial in the form of a tube, and is provided at each end with aplurality of marker carrier portions, to each of which is mounted aradiopaque marker of radiopaque material, in the form of a spoon. Eachof the carriers has a luminal surface, an abluminal surface, and aperipheral surface through the thickness of the stent tube. It is thisperipheral surface which provides one of two complementary matingsurfaces for making the stent/marker attachment. The complementarymarker itself has two major surfaces, one of which is luminal and theother is abluminal, and a peripheral surface around the major surfaces.However, within the area of the major surfaces is a cavity portion. Theperiphery of this cavity defines a female element for engagement with amale portion of the stent tube marker carrier portion, the male andfemale peripheral surfaces providing complementary tapering form-fitsurfaces.

Preferably each such ring of markers has four marker spoons in it.Increasing beyond four reduces the size of each marker. In the expandedconfiguration of the stent, visibility of the stent increases with thephysical area of each separate marker, so large markers are preferredbecause they make the expanded stent more visible.

It is preferred that the markers together make a more or less continuousring around the stent in its small diameter configuration prior to itsdeployment by expansion.

According to the second aspect of the present invention there isprovided a method for making from sheet material a tubular implant, suchas a stent, which expands, during its deployment, from a smaller radiusdelivery disposition to a larger radius deployed disposition, the methodcomprising the steps of:

-   -   1. providing at least one terminal element on one end of a        support of sheet material arranged as a cylinder with its radius        being that of the said delivery disposition;    -   2. presenting the tubular implant in its smaller radius,        end-to-end with the support, such that the terminal element        abuts the implant;    -   3. fixing the terminal element to the implant; and    -   4. parting the terminal element from the support.

One of the problems involved in fixing radiopaque markers to stents isthe difficulty of aligning the markers with the stent in order to fixthe markers to the stent in exactly the right orientation and positionrelative to the stent as such. This second aspect of the inventionameliorates this problem by presenting markers as terminal elements onone end of a cylindrical support of sheet material which has the sameradius as the stent in its unexpanded disposition. This is because it isrelatively easy to arrange in co-linear fashion the cylinder of thestent and the cylinder of the support and, with both of these itemshaving the same radius, the cylindrical end surface of the support wouldbe in abutment with the cylindrical end surface of the stent. Now, ifthe cylindrical end surface of the support exhibits a plurality ofterminal elements which are destined to become elements attached to thestent, the process of fixing these markers to the stent can be effectedby welding the elements to the end of the stent, while they are inend-to-end abutment with the stent end. Then, when this welding step hasbeen completed, it should be a simple further step to part the markerelements from the support cylinder, for example, by laser-cuttingthrough the thickness of the sheet material which forms the support.

It will be appreciated that the terminal elements will have thecurvature of the support cylinder, which curvature will correspond tothe curvature of the stent in its delivery disposition. Thus, when thestent expands to its deployed disposition, and the curvature of theterminal elements remains unchanged, these elements will have a radiusof curvature somewhat smaller than the radius of the expanded stentcylinder. However, this discrepancy in curvature will not be significantbecause the terminal elements will be, to a greater or lesser extent,embedded in the bodily tissue forming the wall of the lumen in which thestent is deployed. Indeed, the elements might have no curvature at all.This would be the case if, for example, the main stent manufacturingsteps are performed on flat sheet material, while it is planar, with thestent lattice then being rolled up for installation into a deliverysystem. The rolling up step would impart a curvature to the stent, butnot necessarily to the attached elements.

The invention is particularly well adapted to the technical field ofshape memory alloy stents, specifically those made of Nitinol, and theattachment to them of terminal marker elements of tantalum.

In order to make Nitinol stents more visible to radiation, by theprovision of tantalum markers, one would wish to import a greater massof tantalum, but without any increase in the wall thickness of the stentat the locations of the markers. The ideal stent has minimal wallthickness, not only for keeping the stented bodily lumen as open tofluid as possible, but also to keep the stent delivery system with assmall a cross-sectional profile as possible. The present inventionfurthers this objective, in the following way.

The cylinder of sheet material which provides the terminal elements andsupport tube is amenable to laser-cutting of the terminal elements outof the material of the tube. Accordingly, virtually all of the materialforming the circumference of the tube is available for contribution tothe making of the terminal elements. The terminal elements can take upthe entire circumference of the support tube, except for the thicknessof the laser cuts between adjacent terminal elements around thecircumference. Accordingly, for the stent in its small radius deliverydisposition, there could be virtually an entire circumference ofradiopaque tantalum marker material provided at each end of the stent,with the only breaks in the continuous ring around the circumferencebeing the laser cuts between adjacent marker elements.

In one specific embodiment, there is laser-cut from the support tube apattern of four terminal marker elements, each extending around onequarter of the circumference of the support tube. Each of these markerelements takes up virtually ninety degrees of the circumference of thestent in its delivery disposition.

The exact shape of the outline of each terminal element, and the exactshape of the abutment surface on it which contacts the correspondingabutment surface of the end of the implant, is a matter of designfreedom and choice. At the moment, for implants which are stents, andattached elements which are radiopaque markers, it is contemplated toprovide each element with more or less straight sides to face theadjacent marker elements around the circumference of the stent, but withan arcuate end surface and a female rebated internal abutment surface toreceive a corresponding arrowhead shape male marker carrier portion onthe end ring of the stent. Such a pattern of shape features is describedin more detail below by reference to the accompanying drawings.

With a male/female interfit of the marker element and stent end ringcarrier portions, with rebated surfaces, and with the respectiveperipheral mating surfaces extending along radial lines to the stentcylinder, a snap fit interengagement of the stent cylinder and supportcylinder can be arranged, further helping to accomplish the objective ofprecise position and orientation of the marker elements relative to thestent cylinder.

In any event, a convenient way to fix permanently and reliably thetantalum marker elements to a Nitinol stent cylinder is bylaser-welding. When laser-cutting the lattice of a stent from a cylinderof sheet material, the line of action of the laser is invariably on aradius of the tubular workpiece. If the co-operating surfaces of thestent, and of its spoons, end elements or markers, are both cut with alaser on a radial line of action, then there will tend to be aself-centering and self-aligning effect when the support tube is offeredup, end-to-end to the stent in its small radius of compressedconfiguration. This effect enhances the value of the method of thepresent invention in building stent assemblies to precise tolerances andwith its end elements securely attached.

For a better understanding of the present invention, and to show moreclearly how the same may be carried into effect, reference will now bemade, by way of example, to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view from the side of a stent tube, looking along a linewhich intersects the long axis of the tube and is perpendicular to itthe stent being in its smaller radius delivery configuration; and

FIG. 2 is the view of FIG. 1, but with the stent in its deployed,relatively large radius disposition;

FIG. 3 is a micrograph taken on a section through the line III-III shownin FIG. 2;

FIG. 4 is a micrograph taken on a section through the line IV-IV shownin FIG. 2; and

FIG. 5 shows schematically a stepwise manufacturing process.

DETAILED DESCRIPTION

Skilled readers will appreciate that the material of the stent tube andits markers lies all in a circular cross-section with a wall thicknessas small as possible, so as to be consistent with the objective ofmaintaining a bodily lumen as open as possible. The stent cylinder canbe formed from seamless tubular starting material, or from flat materialrolled into a tube (which thus exhibits some sort of seam).

Skilled readers will also be well aware that there have been a verylarge number of proposals for strut patterns in the tubularconfigurations of stents. Whereas FIG. 1 shows an expandable strutpattern in a form which is particularly preferred for the presentApplicant, nevertheless any other strut pattern will have points in itwhich define an end to the cylinder of the stent, and therefore willhave points at the ends of the stent cylinder where markers can beattached.

Readers will also appreciate that self-expanding stents are delivered tostenting locations in a radially compressed form, so that the aggregatelength, in the circumferential direction, of all of the markers in anyparticular ring around the axis of the stent tube cannot exceed thecircumference of the stent tube in its compressed deliveryconfiguration. In the embodiment shown in FIG. 1, each of the fourmarkers has a circumferential length just less than the circumferentiallength of three cycles of the zigzag pattern which defines the end ringof the stent cylinder so that, when the stent cylinder is compressed,with all the struts of the zigzag ring laying close to each other, theadjacent radiopaque markers will also lie closely adjacent each other inthe circumferential direction.

As can be seen in FIG. 1, the end ring 12 of the stent cylinder 10 isconstituted by a succession of struts 14 which zigzag their way aroundthe full circumference of the ring 12. There is a vertex 16 where eachtwo successive struts intersect, with the end of the stent cylinderbeing defined by the succession of vertices 16. A marker carrier portion18 is located at every third end vertex 16, and fitted to each carrierportion 18 is a marker element 20. In the illustrated embodiment, thestent is made from Nitinol, nickel-titanium shape memory alloy, and eachmarker element is of tantalum. In other embodiments, the stent could beof stainless steel. The attached elements could be of tantalum,platinum, gold or iridium, for example.

Referring now to FIGS. 3 and 4 together, the tantalum marker 20 has aluminal surface 22 and an abluminal surface 24, with the abluminalsurface 24 being in line with the abluminal surface 26 of the stentcylinder and the luminal surface 22 of the marker being in line with theluminal surface 28 of the stent cylinder. FIG. 4 shows that theperipheral surface 30 of the carrier portion 18 is tapered inwardly fromthe abluminal surface 26 to the luminal surface 28 of the stentcylinder. The marker 20 has a co-operating complementary tapered matingsurface 32, therefore also defining part of a cone with its vertex lyingradially inside the stent cylinder. It will be appreciated thatachievement of the form fit-shown in FIG. 4 is by advancing the carrierportion 18 radially inwardly into the cavity defined by surface 32 ofthe marker 20 until there is a tight fit between the two complementarytapered surfaces 30 and 32, corresponding with a lining up of theluminal and abluminal surfaces of the stent cylinder and marker.

In FIG. 4 surfaces 24 and 26 face a bodily lumen wall. The stentcylinder 10 with its end ring 12 and its carrier portions 18 are servingto hold back the bodily lumen wall tissue from radially inwardencroachment (rightwards in FIG. 4). The tissue presses radially inwardalso on the marker 20, tending to dislodge the form-fit. However, inlaser-welding the tantalum spoon 20 to the Nitinol carrier portion 18,melting and flow of Nitinol around the tantalum spoon achievesre-entrant locking surfaces, as can be seen on the photomicrograph,which effectively resist such dislodging.

The present invention aims to assist the attachment of tantalum markersto Nitinol stents, for example by laser-welding, and make it even morereliable and secure. The melting point of tantalum is around 3000° C.,and that of Nitinol around 1200° C., rendering it difficult to achieve agood bond purely by welding. However, the tapered close fit between thetwo metals, and the flow of Nitinol around the tantalum during welding,achieves a secure mechanical interlock between the stent and the marker20.

It is conventional to form the lattice patterns of Nitinol stents bylaser-cutting. The line of action of a laser for cutting the taperedmating surfaces 30 of the carrier portion 18 in the stent are achievedby aligning the laser in the normal radial direction of intersecting thelong axis of the stent tube.

As to the number of markers in one circumference of the stent, optimumradiopacity is accomplished when the markers at each end of the stentmake up a virtually unbroken solid ring of marker material around thefull circumference. In the case shown there is a marker on every thirdend vertex of the stent, with 4 markers at each end of the stent, and 12zigzag vertices around the circumference of the stent. This, however, isnot to exclude the possibility of fewer markers at each end of thestent, including the extreme case, seen in wo 95/03010, mentioned at thebeginning of this specification, that there is only one marker at eachend of the stent cylinder.

Turning now to the second aspect of the invention, and to the assemblyof the markers 20 onto the stent 10, one can see from FIG. 1 how thefour markers 20 at each end of the stent cylinder form a virtuallyunbroken ring of material having a diameter exactly the same as that ofthe stent cylinder 10 in the delivery disposition of FIG. 1.

FIG. 5 shows the four adjacent markers 56 are all cut from a single tubeof tantalum material having the same radius as the stent cylinder 10, alaser having been used to cut around the periphery of each marker,including the rebated portion in the centre of the marker which receivesthe marker portion 18 of the stent. The only place where the thus cutmarker element 56 remains attached to the carrier tube is at the centraltip 40 (FIG. 1) of the arcuate surface 42 which defines the peripheralend surface of the marker 20 remote from the stent cylinder 10.

A support cylinder 54 which includes the four markers 20, 56 attached attheir tips 40 is offered up to the stent cylinder 10, the two cylindersbeing co-linear and coaxial. There is then a snap fit of the markerportions 18 of the stent 10 into the receiving recess of each marker 20.Once the marker portions 18 are secure within the recesses of therespective markers 20, a laser can be deployed to produce a laser weldbetween the marker portion 18 and the marker 20. During welding; theNitinol adjacent the tantalum marker melts locally and to a limitedextent flows around the tantalum, thereby effectively form-locking themarker to the stent. With this laser welding accomplished, a laser canthen be brought into play, to part at marker tip 40 each individualmarker 20 from the carrier tube 54 which has supported it up to thatpoint. With this parting away of the markers 20 from their carrier tube,the stent can then be separated from the carrier tube, with the markers20 securely welded to the stent 10.

Readers will immediately appreciate from the above description, taken inconjunction with the drawings, that the markers 20 have the general formof a spoon. That is to say, the markers have two major dimensions andone minor dimension, namely, the thickness in the radial direction ofthe stent. The two major surfaces have a length direction in the lengthdirection of the stent and are more or less flat in that direction.However, in the transverse direction, circumferential with respect tothe stent cylinder, the markers are curved so that they exhibit aluminal surface which is concave and an abluminal surface which isconvex. This curvature is also exhibited in the transverse direction ofa cutlery spoon.

Further, each marker 20 has a near end surface in which is somethingakin to the shaft of a cutlery spoon, namely, the marker portion 18 ofthe stent. Opposite this end surface is another end surface, relativelyremote from the stent, which is not attached to the stent and is arcuateon its periphery. This is reminiscent of the arcuate (in the sense ofpresenting an outwardly convex shape) peripheral end surface of acutlery spoon, remote from the shaft of the spoon.

In FIG. 5 are shown seven steps, in FIGS. 5(1) to 5(7), of a process formanufacturing an implant in accordance with the invention, which is astent of Nitinol having at each of its ends a ring of tantalum spoons.

Step 1 is to cut with a laser a tube of Nitinol material in order toproduce a stent precursor 50 having at each ends a ring of four markercarrier portions 52 each having a shape which has some slightresemblance to an arrowhead shape. In the example shown here, theNitinol tube has a wall thickness of 0.24 mm and a nominal diameter of1.6 mm.

FIG. 5(2), showing step 2, shows a tube of tantalum 54 which has thesame 1.6 mm nominal diameter and 0.24 mm wall thickness but a shorterlength than the stent precursor 50. At one end of the tantalum tube 54has been laser-cut a ring of four spoons 56. A narrow bridge of material58 at the tip 40 on the arcuate end surface of each spoon connects eachspoon 56 to the tube 54, and a similar narrow bridge 60 links each spoon56 at its widest point to the corresponding point on the next adjacentspoon 56 on each side. In this way, the spoons are all linked up in aring and each individually still part of the tantalum tube 54.

In FIG. 5(3), step 3 of the manufacturing process includes placing acore 62 inside the tantalum tube 54, and a surrounding sleeve 64radially outside the tube 54. The core 62 and sleeve 64 do not extend asfar as the ring of spoons 56 but terminate just short of that ring.Likewise, Nitinol tube 50 receives a core 66 and a surrounding sleeve 68which again stop just short of the ring of carrier portions 52. In ajig, the two spaced cores 62 and 66 are linked through their outer endsso as to be maintained co-axial and co-linear, which therefore assuresthat the ring of carrier portions 52 and ring of spoons 56 arethemselves co-axial and co-linear. FIG. 5(3) shows each of the carrierportions 52 tilted slightly radially outwardly, to indicate that this isfeasible, for offering up the carrier portions 52 into the correspondingrecesses of the corresponding spoons 56, as explained above, and asshown in FIG. 5(4).

In FIG. 5(4), it is shown how manual manipulation of the carrierportions 52 can be used to get them into the corresponding recesses ofthe spoons 56, when the cores 62 and 66 are brought closer to each otherin the above-mentioned jig. This manual manipulation, of each individualcarrier portion 52 in turn, is carried out manually, under a microscope.

FIG. 5(5) shows the carrier portions 52 duly fitted within thecorresponding recesses of the spoons 56.

FIG. 5(6) differs from the preceding method step of FIG. 5(5) by thepresence of a welding bead 70 which connects each one of the spoons 56with its corresponding carrier portion 52, around the periphery of thearrowhead of the carrier portion 52. This welding bead is a result of alaser-welding step which occurs between illustrated steps 5 and 6 but isnot shown as such in FIG. 5. In itself, it will be familiar to readersskilled in Nitinol stent manufacture.

FIG. 5(7) differs from FIG. 5(6) in that the cores 62 and 66 and therings 64 and 68 have been removed, to leave a ring of spoons 56 dulywelded to one end of the Nitinol tube stent precursor 50. With a laser,the bridges 58 and 60 are cut through, so as to release each spoon fromthe tantalum tube 54 and the spoons adjacent to it.

Clearly, if it desired to place a ring of spoons at the other end of thestent tube 50 then the process can be repeated at this other end.Indeed, in FIG. 5, a ring of carrier portions 72 is shown at the otherend of the stent tube 50.

Once the spoons have been placed as desired on the precursor tube 50 ofthe stent, then this precursor tube can be subjected to the normalsuccessor manufacturing steps, including the step of expanding the stentprecursor to a desired larger diameter and then annealing it at thatdiameter in order to “set” a stent shape in the austenitic phase of theNitinol material, which is the shape that it is desired the stent shouldrevert to, in the body, upon deployment from a stent delivery system.Such a set shape might include a central cylindrical portion of thestent, and flared portions at each end, with the ring of carrierportions 52 and spoons 56 themselves forming part of the flared portionof the end of the stent. As tantalum has a melting point so much higherthan that of Nitinol, there is no likelihood that the Nitinol annealingstep will in any way adversely affect the spoons and welding beads ateach end of the stent cylinder.

The scope of protection of the claims which follow is not to be limitedto the embodiments described in detail above. Readers will appreciatethat the detailed description is to assist in realising embodimentswithin the scope of the claim rather than to set a limit on the scope ofprotection.

1. A method of attaching elements to an axial terminal end of a tubularimplant comprising: providing said elements on one end of a support tubehaving a radius substantially that of the implant in its unexpandedconfiguration, adjacent of said elements unconnected, abutting theimplant and elements end-to-end, fixing the elements to the implant, theelements and implant having tapered mating surfaces tapering in a radialdirection of the implant, and parting the elements from the supporttube.
 2. A method as claimed in claim 1, wherein the elements comprisespoons.
 3. An implant comprising: a wire or sheet material arranged inthe form of a metal tube having a long axis, a luminal surface and anabluminal surface, and a radial wall thickness between said surfaces,the implant carrying within the wall thickness a plurality of separateelements made of an element material other than the wire or sheetmaterial, the elements being disposed at a terminal end of the implant,and the elements and the tube having complementary tapered matingsurfaces extending longitudinally from the terminal end along alongitudinal axis of the tube for achieving a taper form fit of theelements on to the tube along a plane traversing the radial wallthickness.
 4. An implant as claimed in claim 3, wherein each of theelements comprises a spoon.
 5. A medical device, comprising: an implantdefining a longitudinal axis and a terminal implant end; a plurality ofindependent markers; and a plurality of marker carriers each having anarrowhead shape with a barbed arrowhead base end disposed to engage theterminal implant end and an opposing end directed away from the terminalimplant end, wherein a periphery of the marker carrier is taperedinwardly toward the longitudinal axis.
 6. The device of claim 5, thearrowhead shape including at least one barb pointing in a directiontowards the terminal implant end.
 7. The device of claim 6, the at leastone barb defining a gap between the at least one barb and a markercarrier shaft joining the implant and the marker carrier.
 8. A medicaldevice, comprising: an implant defining a longitudinal axis and aterminal implant end; a plurality of separate markers; and a pluralityof marker carriers disposed at the terminal implant end, each of themarker carriers including a tapered periphery, a first portion disposedto engage the terminal implant end, and a second portion, the firstportion disposed between the terminal implant end and the second portionand defining a first direction from the first portion to the secondportion, the first and second portions having widths transverse to thedirection, the first portion width being less than the second portionwidth, the marker carriers including a transition portion defining atransition from the first portion width to the second portion width, thetransition portion including at least one projection disposed to extendfrom the first portion in a second direction opposite to the firstdirection.
 9. A medical device, comprising: an implant defining alongitudinal axis and a terminal implant end; a plurality of markerscircumferentially separated; and a plurality of marker carriers disposedat the terminal implant end, each of the marker carriers including atapered periphery, a first portion disposed to engage the terminalimplant end, and a second portion, the first portion disposed betweenthe terminal implant end and the second portion and defining a directionfrom the first portion to the second portion, the first and secondportions having widths transverse to the direction, the first portionwidth being less than the second portion width, the marker carriersincluding a transition portion defining a transition surface from thefirst portion width to the second portion width, the transition surfacehaving an undulation along a plane orthogonal to the direction.
 10. Amedical device, comprising: an implant defining a longitudinal axis anda terminal implant end; a plurality of markers circumferentiallyseparated; and a plurality of marker carrier disposed at the terminalimplant end, each of the marker carriers including a tapered periphery,a first portion disposed to engage the terminal implant end, and asecond portion, the first portion disposed between the terminal implantend and the second portion and defining a direction from the firstportion to the second portion, the first and second portions havingwidths transverse to the direction, the first portion width being lessthan the second portion width, the marker carrier including a transitionportion defining a transition surface from the first portion width tothe second portion width, the transition surface defining a gap betweenthe first portion and the second portion along a plane orthogonal to thedirection.
 11. A medical device, comprising: an implant defining alongitudinal axis and a terminal implant end; a plurality of markercarriers disposed at the terminal implant end, each of the markercarriers having a wide portion and a narrow portion, the narrow portiondisposed between the wide portion and the implant end, the wide portiondefining an exterior surface disposed in a plane traversing thelongitudinal axis; and a plurality of separate markers, each disposed toengage the exterior surface of the wide portion in order to resistradially-inward movement relative to its respective marker carrier. 12.The device of claim 11, each marker disposed to engage the entireexterior surface of the wide portion within the plane traversing thelongitudinal axis.
 13. The device of claim 11, the narrow portiondefining an exterior surface disposed in a plane orthogonal to thelongitudinal axis, each marker disposed to engage the exterior surfaceof the narrow portion.
 14. A medical device, comprising: an implantdefining a longitudinal axis and a terminal implant end; a plurality ofmarker carriers disposed at the terminal implant end, each of the markercarriers having a wide portion and a narrow portion, the narrow portiondisposed between the wide portion and the terminal implant end; and aplurality of separate markers, each having an exterior surface defininga cavity, at least a portion of a respective one of the marker carriersdisposed within the cavity such that the marker carriers resistradially-inward movement of the markers.
 15. The device of claim 14, thewide portion disposed entirely within the cavity.
 16. The device ofclaim 14, a part of the narrow portion disposed within the cavity.
 17. Amedical device comprising: an implant defining a longitudinal axis and aterminal implant end; a plurality of marker carriers disposed at theterminal implant end, each having an outer peripheral surface disposedin a plane at least in part intersecting the longitudinal axis; and aplurality of separate markers, each having an inner peripheral surfacedisposed in a plane at least in part intersecting the longitudinal axis,at least a portion of the outer peripheral surface abutting at least aportion of the inner peripheral surface along a rebated surface toengage each of the markers with its respective marker carrier, the innerand outer surfaces abutting when an outer circumferential surface ofeach of the marker carriers aligns with an outer circumferential surfaceof its respective marker.
 18. A medical device comprising: an implantdefining a longitudinal axis and a terminal implant end; a plurality ofmarker carriers disposed at the terminal implant end, each having anouter peripheral surface disposed in a plane at least in partintersecting the longitudinal axis; and a plurality of separate markers,each having an inner peripheral surface disposed in a plane at least inpart intersecting the longitudinal axis, at least a portion of the outerperipheral surface abutting at least a portion of the inner peripheralsurface along a rebated surface to engage each of the markers with itsrespective marker carrier, the inner and outer surfaces abutting when aninner circumferential surface of each of the marker carriers aligns withan inner circumferential surface of its respective marker.
 19. A medicaldevice comprising: an implant defining a longitudinal axis and aterminal implant end; a plurality of marker carriers disposed at theterminal implant end, each having an outer peripheral surface disposedin a plane at least in part intersecting the longitudinal axis; and aplurality of unconnected markers, each having an inner peripheralsurface disposed in a plane at least in part intersecting thelongitudinal axis, at least a portion of the outer peripheral surfaceabutting at least a portion of the inner peripheral surface along arebated surface to engage each of the markers with its respective markercarrier, the inner or outer peripheral surfaces defining a tapered edgein a plane traversing the longitudinal axis.
 20. A medical devicecomprising: an implant defining a longitudinal axis and a terminalimplant end; a plurality of marker carriers disposed at the terminalimplant end, each having an outer peripheral surface disposed in a planeat least in part intersecting the longitudinal axis; and a plurality ofunconnected markers, each having an inner peripheral surface disposed ina plane at least in part intersecting the longitudinal axis; at least aportion of the outer peripheral surface abutting at least a portion ofthe inner peripheral surface along a rebated surface to engage each ofthe markers with its respective marker carrier, at least a portion ofthe outer peripheral surface abutting at least a portion of the innerperipheral surface.
 21. A medical device comprising: an implant defininga longitudinal axis and a terminal implant end; a plurality of markercarriers disposed at the terminal implant end and having an outerperipheral surface disposed in a plane at least in part intersecting thelongitudinal axis; and a plurality of disconnected markers, each havingan inner peripheral surface disposed in a plane at least in partintersecting the longitudinal axis, at least a portion of the outerperipheral surface abutting at least a portion of the inner peripheralsurface along a rebated surface to engage each of the markers with itsrespective marker carrier, each marker carrier including a welding areaportion defining the outer peripheral surface, the welding area portionconsisting of a melted portion of the marker carrier.
 22. A method,comprising: inserting a marker carrier disposed on a terminal end of animplant into an internal cavity of one of a plurality of unconnectedmarkers, the cavity defined by a peripheral surface of the one marker;abutting the marker peripheral surface against an exterior surface ofthe marker carrier, the abutting surfaces having a complimentary taperin a direction traversing a thickness of the marker; and joining themarker to the marker carrier.
 23. A method, comprising: aligning aplurality of unconnected markers extending from a tube with a pluralityof respective marker carriers extending from a terminal end of a tubularimplant; inserting the marker carriers into internal cavities of themarkers, the cavities defined by a peripheral surface of the marker;joining each of the markers to the marker carriers at complimentarytapered mating surfaces tapering in a radial direction of markercarrier; and separating the tube from the markers.
 24. A method,comprising: disposing a plurality of unconnected markers in apredetermined position relative to a plurality of respective markercarriers engaging a terminal end of a tubular implant defining alongitudinal axis; maintaining the predetermined position in alongitudinal direction parallel to the axis and in a circumferentialdirection about the axis with opposing mating surfaces of the markersand marker carriers; and maintaining the predetermined position in aradial direction relative to the axis with opposing angled matingsurfaces.
 25. A method, comprising: disposing a plurality of separatedmarkers in a predetermined position relative to a longitudinal axisdefined by a tubular implant disposed with a terminal implant endproximate the markers; disposing a plurality of marker carriersextending from the terminal implant end to abut peripheral edges of themarkers; and aligning the marker carriers relative to the markers byengaging mating surfaces having a cross-sectional taper in a planetraversing the axis.
 26. A method, comprising: disposing a plurality ofseparated markers proximate a terminal end of a tubular implant defininga longitudinal axis; deflecting a plurality of marker carriers extendingfrom the terminal end of the tubular implant away from the axis to aradial distance greater than a radial distance between the markers andaxis; moving the marker carriers to a position radially adjacent themarkers; deflecting the marker carriers toward the axis to a radialdistance equal to the radial distance between the markers and axis; andengaging the markers with the marker carriers at complimentary taperedmating surfaces tapering in a radial direction of the implant.